The Australian Christmas Tree, Nuytsia floribunda, and Its Ingenious Way of Survival

Strange Yet Most Efficient Way of Survival

Nuytsia floribunda, Australian Christmas tree as it is known in its native Southwest Australia is one of most extraordinary plant species that can be found in that region of the Australian continent. It is also one of the tallest, up to 15 m high. At the peak of summer, from late December to January, is when the Christmas tree blooms unlike the other Australian species. Its vivid and fragrant golden orange flowers densely packed in panicles are a spectacular display throughout the arid and dry region where it grows. Looking at the rest of the trees and plants surrounding the Christmas tree it seems odd and yet strange that such a noticeable specimen looks so vigorous and so alive as opposed to the rest that is dry and seems almost dead at that time of the year. You could think that the Christmas tree has found an exclusive source of water unavailable for the rest of the plants. Well, it is half true. In fact, there is not much water accessible to the Christmas tree than for any of plants surrounding it. But, the Australian Christmas tree uses a unique strategy that has revealed itself quite efficient for its survival in such hard conditions. The truth is that the Christmas tree steels water from its neighbouring plants that absorb it from the deep dry soil even before they can use it. When an Australian Christmas tree root finds another root from a different species it develops a cap, called haustorium that firmly attaches to that root. It does not take long to surround the neighbour’s root completely forming a white ring. On the opposite side of the cap that attaches to the root a guillotine scissor-like growth forms. This unique structure grows towards the host root and slices it in order to attach into the xylem vessels that transport water and nutrients to the host plant body. Simultaneously, the cap tissue develops xylem vessel elements that spread inside the host wounded tissue and drive water to the Australian Christmas tree. On doing this thousand of times to all the neighbouring plant roots that it reaches, the Australian Christmas tree manages to get an almost infinite source of water and nutrients just for its private use. Although it obtains little from every single host plant that it attaches to. The advantage of this strategy lies thus in the number of host roots that the Australian Christmas tree can feed upon. Basically the Australian Christmas tree has all its neighbour plants working for it. On searching for host roost the Christmas tree roots can spread over 100 m or more. Hence a single Christmas tree can cover an extensive area parasitizing a vast number of different plant species,mostly shrubs and herbs. To be that successful and in order to manage to grow to those heights the Christmas tree attacks on a vast number of different species from trees, bushes, small plants and even smaller such as grasses. It as also been observed to attack alien species brought to Australia like roses or carrots. In fact it acts on a totally indiscriminate way. The irony of all this, and quite funny in my opinion, being also one of the things that makes the Australian Christmas tree so unique, is that is bigger than most of its hosts that it parasitizes, if not the biggest you can find there where it thrives. Usually one single parasite lives or feeds from one single host and so it is does not get bigger than the host it depends upon. Especially, if the parasite lives inside the host. The Australian Christmas tree on having and army of hosts working for it can thus thrive and grow much more than any of its hosts, as the likelihood of having more water available than any of its hosts is much higher for the Australian Christmas tree. This tree is thus considered the biggest parasitic plant in the world. So, when looking at one big Australian Christmas tree, like the one in the photo, you can think that the tiny grasses next to it will most certainly be supplying water to the big and healthy Australian Christmas tree. Nature can be so cruel. I know.

Haustoria and the white ring formed by Christmas tree roots on its host's roots.

The scissor-like structure that slices the host root.

When More Becomes Too Much

Some years ago, Australian airspace scientists decided to install a receiving station in Western Australia. Several equipment devices were installed and connected through underground cables spread over an extensive area. It did not take long for interruptions, breakdowns and communication problems to appear after the system network started to work. The Australian Christmas tree was easily pointed as the villain and main responsible. Is was found that in fact the Australian Christmas tree was attacking the cables penetrating the plastic envelope and reaching the electrical copper wires. The problem was greatly announced so that the telecommunication companies working in Western Australia admitted that several hundred of km of communication cables would likely be attacked between 40 to 50 times per year. Even the fiber optic cable that came afterwards did not resist the attack of the fearless Australian Christmas tree. The only solution while using underground cables, although more expensive, was to use thicker cables with such a wide plastic covering that would be impossible for the Christmas tree root to form its deadly ring and thus surround the cable.

Parasitism in the Plant Kingdom

The Australian Christmas tree, Nuytsia floribunda, belongs to Loranthaceae family, in which many of its species are hemiparasites. Hemiparasites are plants that for can live for some part of their life cycle autonomously, but later they need a host in order to complete that life cycle, usually in the adult reproductive stage. This means that they are capable of photosynthetic activity and so at some level they are self-sufficient, like most plants. That is also the case with Nuytsia floribunda. Its seeds germinate readily and seedlings are easy to grow for a year or two to become a bush. After that time it must attach to its neighbouring plants in order to survive. It is when its growth changes and its vigorous behaviour is revealed. For this reason the Australian Christmas tree is classified as an obligate parasite in order to complete its life cycle, i.e. becoming and adult plant and then reproduce. In this case, it is a root parasite. Most of the parasitic species of the Loranthaceae family are hemiparasitic but they attach to the stem or branches of the host plant. Nuytsia floribunda is an exception as it attaches to the root of its hots, depending totally on its host plants in order to obtain water and mineral nutrients from the soil. The Australian Christmas tree is also popular as the sap that exudates from a wound can be collected. It is sweet and eaten raw as gum.

Parasitic Plants: The Sideshow of the Botanical Worl...Parasitic plants are a diverse group of plants that adpated and specialized in obtaining water and nutrients from other plants. They are distributed worldwide and produce some of the more amazing structures in the plant world. They can be a serious m